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Changed the documentation to reflect the new fastcall/cdecl reality.

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Greg King
2015-03-13 05:40:55 -04:00
parent a798b1d648
commit 604a5b4447
2 changed files with 60 additions and 34 deletions
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doc/cc65.sgml
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@@ -3,7 +3,7 @@
<article>
<title>cc65 Users Guide
<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
<date>2000-09-03, 2001-10-02, 2005-08-01
<date>2015-03-13
<abstract>
cc65 is a C compiler for 6502 targets. It supports several 6502 based home
@@ -549,9 +549,9 @@ and the one defined by the ISO standard:
be passed as parameters by value. However, struct assignment *is*
possible.
<p>
<item> Part of the C library is available only with fastcall calling
conventions (see below). It means that you must not mix pointers to
those functions with pointers to user-written, not-fastcall functions.
<item> Most of the C library is available only with the fastcall calling
convention (see below). It means that you must not mix pointers to
those functions with pointers to user-written, cdecl functions.
<p>
<item> The <tt/volatile/ keyword doesn't have an effect. This is not as bad
as it sounds, since the 6502 has so few registers that it isn't
@@ -589,29 +589,54 @@ This cc65 version has some extensions to the ISO C standard.
<ref id="inline-asm" name="see there">.
<p>
<item> There is a special calling convention named "fastcall".
The syntax for a function declaration using fastcall is
<item> The normal calling convention -- for non-variadic functions -- is
named "fastcall". The syntax for a function declaration that
<em/explicitly/ uses fastcall is
<tscreen><verb>
&lt;return type&gt; fastcall &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
or
<tscreen><verb>
&lt;return type&gt; __fastcall__ &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
An example would be
<tscreen><verb>
void __fastcall__ f (unsigned char c)
</verb></tscreen>
The first form of the fastcall keyword is in the user namespace and can
therefore be disabled with the <tt><ref id="option--standard"
<tscreen><verb>
&lt;return type&gt; fastcall &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
or
<tscreen><verb>
&lt;return type&gt; __fastcall__ &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
An example would be
<tscreen><verb>
void __fastcall__ f (unsigned char c)
</verb></tscreen>
The first form of the fastcall keyword is in the user namespace and can
therefore be disabled with the <tt><ref id="option--standard"
name="--standard"></tt> command line option.
For functions declared as <tt/fastcall/, the rightmost parameter is not
pushed on the stack but left in the primary register when the function
is called. This will reduce the cost when calling assembler functions
significantly, especially when the function itself is rather small.
<p>
For functions that are <tt/fastcall/, the rightmost parameter is not
pushed on the stack but left in the primary register when the function
is called. That significantly reduces the cost of calling functions.
<p>
<item> There is another calling convention named "cdecl". Variadic functions
(their prototypes have an ellipsis [<tt/.../]) always use this
convention. The syntax for a function declaration using cdecl is
<tscreen><verb>
&lt;return type&gt; cdecl &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
or
<tscreen><verb>
&lt;return type&gt; __cdecl__ &lt;function name&gt; (&lt;parameter list&gt;)
</verb></tscreen>
An example would be
<tscreen><verb>
void __cdecl__ f (unsigned char c)
</verb></tscreen>
The first form of the cdecl keyword is in the user namespace and can
therefore be disabled with the <tt><ref id="option--standard"
name="--standard"></tt> command line option.
For functions that are <tt/cdecl/, the rightmost parameter is pushed
onto the stack before the function is called. That increases the cost
of calling those functions, especially when they are called from many
places.
<p>
<item> There are two pseudo variables named <tt/__AX__/ and <tt/__EAX__/.
Both refer to the primary register that is used by the compiler to
@@ -663,7 +688,7 @@ This cc65 version has some extensions to the ISO C standard.
</verb></tscreen>
Since the variable is of type <tt/void/ you may not use it as is.
However, taking the address of the variable results in a <tt/void*/
However, taking the address of the variable results in a <tt/void */
which may be passed to any function expecting a pointer.
See the <url url="geos.html" name="GEOS library document"> for examples